1 
2 .globl	_xinc
3 _xinc:
4 	movl 4(%esp), %eax
5 	lock incl 0(%eax)
6 	ret
7 
8 .globl	_xdec
9 _xdec:
10 	movl 4(%esp), %eax
11 	lock decl 0(%eax)
12 	jz iszero
13 	movl %eax, 1
14 	ret
15 iszero:
16 	movl %eax, 0
17 	ret
18